linux-kernel - Re: [v5 PATCH] arm64: mm: force write fault for atomic RMW instructions

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Message-ID: <20240823095905.GA31592@willie-the-truck>
Date: Fri, 23 Aug 2024 10:59:06 +0100
From: Will Deacon <will@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Yang Shi <yang@...amperecomputing.com>,
	"Christoph Lameter (Ampere)" <cl@...two.org>,
	anshuman.khandual@....com, david@...hat.com,
	scott@...amperecomputing.com, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [v5 PATCH] arm64: mm: force write fault for atomic RMW
 instructions

On Wed, Aug 21, 2024 at 11:18:42AM +0100, Catalin Marinas wrote:
> My view (as kernel maintainer) is that there aren't strong enough
> arguments for merging this patch. It does show an improvement in
> specific cases but the downside is the risk of affecting other cases
> (plus additional maintenance cost, though I'd expect the opcode checking
> to remain the same). I do think the architecture should be changed so
> that the kernel gets the right information in the fault handler but it
> would be a while before such feature appears in hardware.

I agree. This patch is a kludge to work around a bad assumption in OpenJDK
which can be (has been?) easily fixed in userspace.

Will